The present invention relates generally to the photocopying of documents, and is illustrated as applied to the copying of documents by electrostatic photography. More particularly, the present invention is directed to an improvement in the copying of duplex documents, and by the term "duplex documents" is meant a document wherein information is contained on both sides of the document sheet. Further, the present invention contemplates the reproduction of duplex documents as duplex copy, wherein both sides of the copy sheet are utilized to reproduce the two sides of the original duplex document.
The electrostatic photocopying process is well known. In one common xerographic form of electrostatic photocopying, an optical image of a document to be copied is applied to a uniformly charged photoconductive plate or photoreceptor, causing the plate to discharge in those areas which are struck by light. As a result, an electrostatic latent image of the document is formed on the photoreceptor plate. This latent image may then be developed to a visible image by the selective attraction of electroscopic toner particles to the charged areas of the latent image. Usually, the toner particles of the developed image are transferred from the photoreceptor to a receiving copy sheet so the photoreceptor can be re-used, and the transferred toner particles may then be fused to the copy sheet to form a permanent copy of the document.
Many documents carry information on both sides of the document sheet. To copy both sides of such duplex documents in the conventional mode of copier operation, first one side of the document is exposed to the copier so that an optical image of the first side is applied to the photoreceptor, then the document is turned over to expose the second side to the copier. Typically each side of the document is reproduced on a separate copy sheet, resulting in two sheets of copy for each single sheet of duplex document.
In accordance with the present invention, a duplex document is placed in a sandwich platen which is transparent of both sides, and then one side of the document sheet is exposed to the copier through one side of the platen, followed by exposure of the other side of the document through the other side of the platen. Dual optical paths are provided, so that each side of the document can be exposed to the copier automatically, and without the necessity of turning the document over. In addition, it is contemplated that the copy sheet will be processed through the copier twice, being turned over between the two traverses, so that an image of one side of the document will be reproduced on one side of the copy sheet, and an image of the other side of the document will be reproduced on the other side of the copy sheet, to provide a duplex copy of the original duplex document.
It is therefore one object of the present invention to provide for the sequential exposure of the two sides of a duplex document to a copier.
Another object of the present invention is to provide for the sequential exposure of the two sides of a duplex document to a copier, by utilizing a sandwich platen for the document, which is transparent on both sides, so each side of the document can be exposed to the copier through dual optical paths.
Sitll another object of the present invention is to provide for the foregoing sequential exposure of a duplex document, and the reproduction thereof as a duplex copy.
Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of several illustrative specific embodiments of the invention.